I think you may have the wrong pronoun there. The simplest translation of both "kākou" and "kāua" is "we/us". "Kāua" means just two people, the speaker and the listener. "Kākou" means more than two people, including the speaker, the listener, and others. Because of the all inclusive nature of "kākou", it is sometimes translated as "everyone" or "all of us".
There are more versions of "we/us" that do not include the listener, but those are not used until later in the course.
The phrase "Mālama pono" can be translated as "Take good care" (or just "take care"), with the word "pono" showing an emphasis on the quality of the mālama-ing. It is a phrase that is commonly heard when people are saying goodbye to each other. That's why it is taught in this unit, which is centered on greetings and goodbyes.
In the above phrase, pono is used like an adverb. This kind of usage is encountered in other common phrases like "Nānā pono" -> "Look well" or "Look closely".
You are right that "kāua" is a pronoun that refers to two people. Those two people are yourself and the person you are talking to (a.k.a. the listener).
you can make the accents by going to settings-then general- keyboard and change it to the language that you want it to be and then if you hold the circle at the bottom of the keyboard on your screen you can easliy change it to any language you want that goes for a phone or ipad.